Recent experimental results on optical properties of GaN and related materials are discussed. Photoluminescence data of free excitons for sufficiently pure GaN samples demonstrate the dominance of excitonic recombination well above room temperature. Transient PL data give a radiative lifetime of about 200 ps for the A-exciton at 2 K in strain-free samples. A corresponding value of about 2 ns at room temperature is extrapolated. Radiative lifetimes for bound excitons are measured as about 250 ps for shallow donors and about 1.5 ns for shallow acceptors. Photoluminescence spectra from the 2D electron gas at a GaNAlGaN heterointerface are also demonstrated.